Where '15 cigarettes a day' comes from, and the paper it isn't in

“The mortality impact of being socially disconnected is similar to that caused by smoking up to 15 cigarettes a day, and even greater than that associated with obesity and physical inactivity.”

That sentence is from the U.S. Surgeon General’s 2023 advisory on loneliness, and it carries a superscript 4 after the word “day.” I read it in a search excerpt of the advisory, because the HHS server refused my download of the PDF, so I could not open footnote 4 myself. Everything below is an attempt to follow that number back to a paper I could open.

The short answer

The comparison traces to Julianne Holt-Lunstad, Timothy Smith and Bradley Layton, “Social Relationships and Mortality Risk: A Meta-analytic Review,” PLoS Medicine 7(7): e1000316, published July 27, 2010. It pooled 148 studies and 308,849 participants and found an odds ratio of 1.50 (95% CI 1.42 to 1.59) for survival among people with stronger social relationships.

The paper never says “cigarettes per day.” I read the full text and searched it. The word “cigarette” appears once, inside a 1988 quotation used as an epigraph. The per-day figure came afterward, and the researcher’s own site says where it came from.

Which paper gets the credit

A lot of writing pins the cigarette line on a 2015 paper. Holt-Lunstad, Smith, Baker, Harris and Stephenson, “Loneliness and social isolation as risk factors for mortality,” Perspectives on Psychological Science (2015), is a different analysis, narrower in scope. Its abstract reports odds ratios of 1.29 for social isolation, 1.26 for loneliness and 1.32 for living alone, “corresponding to an average of 29%, 26%, and 32% increased likelihood of mortality.” The abstract ends by calling the influence “comparable with well-established risk factors for mortality.”

I read that abstract but not the full 2015 text, which is paywalled, so I cannot say what the body of the paper does with smoking. What I can say is that the abstract contains no cigarette comparison.

Holt-Lunstad’s own page on the topic (I could only get a machine summary of it, not the raw text) attributes the figure to the 2010 paper. As that summary describes it, the social-connection effect was set against previously published estimates for other risk factors, including smoking. The same page reportedly adds two caveats. The original number combined several measures of social connection, with loneliness as only one. And the smoking estimate covers moderate daily smoking, up to 15 cigarettes, with no precise estimate for the popular “two packs a day” version.

What the 2010 paper actually contains

The comparison in the paper is a figure, not a sentence. Figure 6 plots the effect of social relationships next to effect sizes drawn from other meta-analyses, labeled A through I in the caption. The reference list shows who they came from: Shavelle and colleagues (2008) on smoking habit and mortality, Critchley and Capewell (2003) on smoking cessation in patients with coronary heart disease, Holman and colleagues (1996) on alcohol, and Katzmarzyk and colleagues (2003) on physical inactivity and excess adiposity.

The words in the paper are these: “The magnitude of this effect is comparable with quitting smoking and it exceeds many well-known risk factors for mortality (e.g., obesity, physical inactivity).”

Two things follow. The comparator is quitting, and at least one of the cessation estimates comes from people who already had heart disease. And “15 cigarettes” is a translation someone made between that figure and a dose of smoking. It may be a fair translation. It is not a result the 2010 paper reports.

Claim against source

Popular claim	Where it appears	What the source I read says
Social disconnection is like smoking up to 15 cigarettes a day	Surgeon General advisory, 2023 (excerpt only)	No per-day figure in the 2010 full text; comparison is a figure against published meta-analyses
People with strong relationships have a 50% greater chance of survival	Holt-Lunstad et al., 2010, abstract	OR 1.50, odds not probability, averaged over many measure types
Loneliness raises death risk by 26%	Holt-Lunstad et al., 2015, abstract	OR 1.26 for loneliness, 1.29 isolation, 1.32 living alone, with confounds controlled
Comparable to quitting smoking, bigger than obesity and inactivity	Holt-Lunstad et al., 2010, conclusion	Quoted nearly verbatim; wording is “comparable” and “exceeds many”
Relationships rival cholesterol and smoking as a health factor	House, Landis and Umberson, Science, 1988	Older than both papers; quoted by the 2010 authors as their opening epigraph

The cholesterol line is older than Harvard

The last row matters if you came here from the viral version about relationships beating cholesterol. The 2010 paper opens with this epigraph from House, Landis and Umberson in Science, 1988: “Social relationships, or the relative lack thereof, constitute a major risk factor for health—rivaling the effect of well established health risk factors such as cigarette smoking, blood pressure, blood lipids, obesity and physical activity.”

So the framing of relationships as a risk factor on a par with the clinic’s usual suspects predates Holt-Lunstad’s meta-analysis by 22 years. The 2010 authors describe the 1988 piece as a review of five large prospective studies and say their own work covers nearly 30 times as many. The Harvard Study of Adult Development has its own version of the claim and its own paper trail.

What was measured, and what wasn’t

The headline 1.50 is an average across very different yardsticks. The paper’s Table 4 and abstract show the spread. Complex measures of social integration, which bundle several kinds of tie into one score, gave 1.91 (95% CI 1.63 to 2.23). A bare yes-or-no for living alone gave 1.19 (95% CI 0.99 to 1.44), an interval that includes no effect at all.

The authors argue their overall figure may be an underestimate. Many studies used single-item measures, “yet the magnitude of the association was greatest among those studies utilizing complex assessments.” Most measures also ignored relationship quality, “thereby assuming that all relationships are positive.”

On cause, the paper is plain. Its studies of healthy community samples suggest that people with strong relationships tend to stay alive longer. Then: “However, causality is not easily established. One cannot randomly assign human participants to be socially isolated, married, or in a poor-quality relationship.”

There is also an age to the evidence. The 2010 literature search ran from January 1900 to January 2007, and it covered English-language reports, so a figure quoted in 2026 as if it were current rests on studies that are at least nineteen years old. The 2015 analysis searched January 1980 to February 2014. Holt-Lunstad’s page says many more studies have appeared since, with consistent results, and that her lab is working on updating the comparison. I have not read those newer studies.

The paper also cannot tell you about your goals, your mornings, or your next six months. The outcome was death, measured over an average of years in a population averaging about 64 years old at the start.

Using the finding without stretching it

Nothing here tests an intervention. What follows is my inference from how the paper’s measures behaved.

The highest odds ratio went to scores that counted several kinds of connection together. A single gesture, one big reunion or one confession, is not what those scores capture. A regular rhythm of contact with a handful of people is closer to what they were built to detect. That fits the paper’s own comparison, in which received support (being helped) predicted survival less well than integration, and its suggestion that using naturally occurring relationships may work better than hired support. It does not prove that texting more often prolongs life.

For a goal that keeps slipping, the bridge is mine and not the study’s. If a friend knows roughly when you are supposed to be up, there is a reason for a tiny, regular exchange to exist between you, with no need for a dinner to be planned. DontSnooze is one way to arrange that, since it makes a few chosen friends the audience for whether your morning happened. Whether that counts as the kind of tie the 2010 studies measured is unknown, and I would not claim it does.

Small and repeated also matches what the paper could measure. A scheduled weekly call, a recurring walk, a shared check-in thread and a daily acknowledgment all produce counts of contact that a complex measure would register. A heroic annual trip registers as one event. The research on goal monitoring points in a compatible direction for a different reason: its pooled effects were larger when progress was recorded and reported.

What I could not close

The chain has one open link. The Surgeon General’s sentence cites footnote 4, and I did not see which paper that footnote names. Holt-Lunstad’s page says the figure rests on the 2010 analysis, and the 2010 full text supports the comparison to smoking cessation, to obesity and to physical inactivity. A separate HHS press-release line putting the premature-death increase at “more than 60%” turned up in a search excerpt, and I could not open the release to see which source it uses. That figure matches neither 1.50 nor the 2015 abstract’s 29%, 26% and 32%.

If you cite the claim, cite the 2010 paper for the odds ratio and the comparison to quitting smoking, cite the 2015 paper for the loneliness-specific 26%, and treat “15 cigarettes a day” as a later translation, which the researcher’s own page attributes to the 2010 analysis and which the advisory repeats.

The mechanism by which close others might help rather than merely accompany you is a narrower claim, examined in the Michelangelo phenomenon paper.